Mahalo is a Hawaiian

Hawaiian language

The Hawaiian language is a Polynesian language that takes its name from Hawaii, the largest island in the tropical North Pacific archipelago where it developed. Hawaiian, along with English, is an official language of the state of Hawaii...

 word meaning thanks, gratitude, admiration, praise, esteem, regards, respects. According to the Pukui and Elbert Hawaiian Dictionary, it is derived from the Proto-Polynesian

Proto-Polynesian language

Proto-Polynesian, , is the hypothetical proto-language from which all the modern Polynesian languages descend. Historical linguists have reconstructed the language using the comparative method, in much the same manner as with Proto-Indo-European and Proto-Afro-Asiatic...

 *masalo.

Some sources support that the meanings 'thanks' and 'gratitude' were appended to the word following contact. While the word mahalo is found in Lorrin Andrews

Lorrin Andrews

Lorrin Andrews was an early American missionary to Hawaii and judge. He opened the first post-secondary school for Hawaiians called Lahainaluna Seminary, prepared a Hawaiian dictionary and several works on the literature and antiquities of the Hawaiians. His students published the first newspaper,...

' 1865 dictionary, the English-Hawaiian section does not provide any Hawaiian word intended to mean gratitude or thanks.
Also, early visitors noted that the Hawaiians were generous and grateful people, but had no word to express gratitude or to say "thank you."